1. Field of the Invention
This invention relates to safety subs for tool strings used in downhole gravel packing, and more particularly, to a safety sub selectively positionable in a rotational or a non-rotational mode.
2. Description of the Prior Art
The typical gravel packing tool string has a liner screen which is positioned adjacent the well formation to be packed and a gravel packer positioned above the screen. Means are included between the packer and screen as necessary for allowing movement of the tool string for unsetting the packer after gravel packing and for releasing the screen from the tool string so that the packer and other tool string elements may be removed from the hole while leaving the gravel packed liner screen in place. On some occasions, the means for releasing may fail to function, typically because sand gets into the mechanism. If this occurs, another method of removing the packer and tool string must be used.
Many packers require rotation for unsetting from the well bore. Because the gravel packed liner screen is stationary after the gravel packing, and rotation of the screen is extremely undesirable, swivel means are provided between the liner screen and packer so that rotation may occur above the swivel for unsetting the packer, while such rotation is not transmitted to the liner screen.
Swivel joints have been developed which include a shear connection therein so that if the releasing means fails to operate, an upward pull on the tool string will shear the shear connection without disturbing the location of the liner screen. Thus, all portions of the tool string, including the packer, above the shear connection in the swivel joint may then be removed from the hole.
For packers which require lifting for unsetting, a clutch joint is typically used. The clutch joint will not transmit rotation to the liner screen while unsetting the packer, but will transmit rotation for rotational disengagement from the liner screen after unsetting of the packer. A swivel joint is not required, and usually no shear joint is employed.
There is a need for shear joints in cases even where rotational disengagement from the screen is utilized. Also, because it may not be known which type of packer may be required or desired, there is a need for a shearable swivel joint, or safety sub, which can be selectively positioned in either a rotational mode or a non-rotational mode. The present invention provides such an apparatus.